For example, the Ar for helium is 4.0, and the A r for carbon is 12.0. This means that carbon atoms have three times the mass of helium atoms. To calculate the M r for a substance: work out how ...

The size of the atoms and their mass has a lot to do with the density of the substance Another factor is how the atoms are arranged in the substance. Polyethylene is made up only of carbon and ...

As they studied atomic disintegration, they kept seeing that the atomic number (number of protons in the nucleus, equivalent to the positive charge of the atom) was less than the atomic mass ...